Sensor for monitoring of ethanol

Abstract

The subject invention provides devices, and methods of making and using the same, for the non-invasive detection of ethanol in a sample. In specific embodiments, the fuel cell based ethanol detector of the subject invention is capable of measuring the concentration of ethanol vapor in the presence of water vapor, which is known to confound signal readings in conventional detectors. Advantageously, the electrochemical sensors provided herein are highly stable and accurate, especially suitable for low-cost, continuous monitoring of ethanol content in transdermal perspiration samples.

We claim: 
     
       1. A fuel cell based sensing device for continuously detecting the concentration of ethanol vapor in a sample, comprising:
 a sensor unit comprising a working electrode as an anode, a counter electrode as a cathode, a reference electrode, and a polymer electrolyte membrane, the anode and the cathode being separated by, and respectively in electrical contact with, the polymer electrolyte membrane, the reference electrode being in electrical contact with the polymer electrolyte membrane and disposed adjacent to, though separated from, the counter electrode; 
 circuitry capable of controlling the potential applied to the sensor unit; and 
 circuitry capable of measuring the current output of the sensor unit; 
 wherein the sensor unit is capable of separating signals produced by ethanol from those produced by background humidity. 
 
     
     
       2. The device according to  claim 1 , wherein the polymer electrolyte membrane is a proton exchange membrane (PEM). 
     
     
       3. The device according to  claim 1 , wherein the working electrode and the counter electrode each includes an active surface area, the active surface area of the working electrode being smaller than the active surface area of the counter electrode. 
     
     
       4. The device according to  claim 1 , wherein the sample is a product of a human transdermal diffusion process. 
     
     
       5. The device according to  claim 4 , the sample being skin perspiration. 
     
     
       6. The device according to  claim 1 , wherein the electrodes comprise a material selected from iron, gold, platinum, carbon, and one or more of these materials combined. 
     
     
       7. The device according to  claim 6 , wherein the working electrode comprises stainless steel. 
     
     
       8. The device according to  claim 6 , wherein each of the counter and the reference electrodes comprises nickel. 
     
     
       9. The device according to  claim 1 , further comprising a thin coating of ethanol-permeable membrane in electrical contact with the working electrode. 
     
     
       10. A method of continuously detecting the concentration of ethanol vapor in a skin perspiration sample collected from a human subject, the method comprising:
 contacting a sample, the sample optionally comprising water vapor, with a fuel cell based sensing device comprising a sensor unit comprising a working electrode as an anode, a counter electrode as a cathode, a reference electrode, and a polymer electrolyte membrane, the anode and the cathode being separated by, and respectively in electrical contact with, the electrolyte, the reference electrode being in electrical contact with the polymer electrolyte membrane and disposed adjacent to, though separated from, the counter electrode; circuitry capable of controlling the potential applied to the sensor unit; and circuitry capable of measuring the current output of the sensor unit, wherein the sensor unit is capable of separating signals produced by ethanol from those produced by background humidity, and wherein the electrodes comprise a material selected from iron, gold, platinum, carbon, and one or more of these materials combined; 
 Obtaining and storing the open-circuit potential (OCP) of the sensor unit by scanning a first range of voltage across the sensor unit; 
 comparing the OCP to a threshold value characteristic to the material employed in the working electrode; and 
 applying the OCP across the working and the reference electrodes while conducting a series of amperometric measurements; 
 wherein, 
 if the OCP is less than the threshold value, the amperometric data are fitted against a pre-determined calibration curve to remove the signals arising from humidity in the surrounding environment and the concentration of ethanol is subsequently determined; and 
 if the OCP is greater than the threshold value, the concentration of ethanol is directly determined based on the amperometric data. 
 
     
     
       11. The method according to  claim 10 , wherein the polymer electrolyte membrane is a proton exchange membrane (PEM). 
     
     
       12. The method according to  claim 10 , wherein the working electrode comprises stainless steel. 
     
     
       13. The method according to  claim 10 , wherein each of the counter and the reference electrodes comprises nickel. 
     
     
       14. The method according to  claim 10 , wherein the device is placed in direct contact with the skin surface of the subject. 
     
     
       15. The method according to  claim 10 , wherein the working electrode comprises stainless steel and each of the counter and reference electrodes comprises nickel. 
     
     
       16. A device for measuring blood alcohol content (BAC) in a skin perspiration sample collected from a human subject, comprising:
 a fuel cell based sensing device comprising a sensor unit comprising a working electrode as an anode, a counter electrode as a cathode, a reference electrode, and a polymer electrolyte membrane, the anode and the cathode being separated by, and respectively in electrical contact with, the polymer electrolyte membrane, the reference electrode being in electrical contact with the polymer electrolyte membrane and disposed adjacent to, though separated from, the counter electrode; circuitry capable of controlling the potential applied to the sensor unit; and circuitry capable of measuring the current output of the sensor unit, wherein the sensor unit is capable of separating signals produced by ethanol from those produced by background humidity, and wherein the electrodes comprise a material selected from iron, gold, platinum, carbon, and one or more of these materials combined;
 a means of displaying the ethanol concentration measured with the sensing device; and 
 
 circuitry capable of processing and analyzing the ethanol concentration data output by the sensing device. 
 
     
     
       17. The device according to  claim 16 , further comprising an electronic platform coupled to the sensing device for receiving user input. 
     
     
       18. The device according to  claim 16 , comprising a casing for enclosing the sensing device, the casing being adapted to a format selected from wearable accessories, apparels, shoes, and vehicular accessories. 
     
     
       19. The device according to  claim 16 , comprising a power supply. 
     
     
       20. The device according to  claim 16 , wherein the working electrode comprises stainless steel and each of the counter and reference electrodes comprises nickel.